Pumping capability and particle balance in W7-X: a self-consistent 3D study

The W7-X stellarator, presently under construction in Greifswald will be equipped from the beginning with an open island divertor designed for stationary operation. In order to optimize the W7-X cryopumping system for an efficient particle control with good confinement in long-pulse operation, simulations are performed with the 3D EMC3-EIRENE plasma edge transport code. The establishment of stationary particle balance crucially depends on the divertor pumping efficiency, which, for a given particle input, sets a lower limit to the plasma density at the separatrix. This paper presents a self-consistent study with EMC3-EIRENE code on the particle balance and pumping capability of W7-X at stationary conditions for relevant ranges of magnetic configurations (ι = 5/5,5/4) and plasma parameters. Specifically, the pumping and recycling fluxes are obtained and lower limits for separatrix density are estimated for three major magnetic configurations with the required pumping parameters in various operating conditions.